“These night wakings could be relatively short — only five to ten minutes — but they disrupt the natural sleep rhythm,” said researcher Avi Sadeh of Tel Aviv University’s School of Psychological Science. “Our study is the first to demonstrate seriously deleterious cognitive and emotional effects.”

To determine those effects, the researchers recruited students to wear devices that monitored their sleep for two nights. On the first night, the participants slept eight hours, uninterrupted. On the second night, they received four phone calls during the night. After each of the calls, they had to complete online tasks for 10-15 minutes before going back to sleep.

When they woke after the second night, the students had a tougher time completing computer tasks that assessed attention. They were also more likely to report waking in a negative mood. Overall, the researchers estimated that interrupted sleep is equivalent to no more than four consecutive hours of sleep.

And that’s after just one night.

“But we know that these effects accumulate and therefore the functional price new parents — who awaken three to ten times a night for months on end — pay for common infant sleep disturbance is enormous,” said Sadeh, who advises sleep-deprived parents at a sleep clinic.

The good news? Sadeh is studying interventions for infant sleep disturbances.